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Possibilities of using a polymer inhibitor for intensification of water desalination by reverse osmosis T.V. Knyazkova, A.A. Kavitskaya Institute of Colloid and Water Chemistry, Ukrainian National Academy of Sciences, 42 Vernadsky pr., Kiev-142, 03680 Ukraine In reverse osmosis desalination of water different methods are applied to prevent the deposition of crystalline inorganic solids (scaling) on membranes. The most wide-spread method for scaling control is utilization of inhibitors, such as sodium hexametaphosphate. During last years an interest for using polymers, as inhibitors, to control scaling in desalination of water is constantly increasing. In this paper the possibilities of using a polymer, sodium carboxymethylcellulose (Na-CMC), for intensification of water desalination with high concentration of calcium sulphate are examined. In reverse osmosis (RO) of NaCL solutions containing CaSO4, included saturated and oversaturated concentrations, a high stabilizing action of Na-CMC is observed. It is shown that Na-CMC additives into the solutions (in quantities from several to tens mg per litre) prevent or slow down the formation of crystalline deposits on cellulose acetate and polyamide composite membranes and substantially decreases flux decline. In the presence of Na-CMC an influence of such factors, as CaSO4 concentration, chemical nature of membrane surface, membrane porous structure or hydrodynamic conditions, on scaling is relaxed. Moreover, the initial membrane performance can be restored by simple water rinsing. When adding Na-CMC an improvement of membrane performance is observed in reverse osmosis of Na-CMC solutions containing simultaneously such deposit-forming components, as calcium sulphate and Fe (III) hydroxide. In this case the positive effect of polymer additive is associated with changes in the deposit composition and its structure. Using Na-CMC as an inhibitor, a high efficiency of ultrafiltration (UF) for pretreatment of salt water with high calcium hardness can be obtained. It is shown that in dead-end UF on cellulose acetate membranes, in the presence of Na-CMC additive, the concentration of saturated CaSO4 solution is achieved by more the twice without deposition of the crystalline solid. Parallel with the inhibiting action, under definite conditions, Na-CMC is able to modify the surface of RO and UF membranes and to increase salt retention. In the presence of Na-CMC additive, the salt retention showed by the reverse osmosis cellulose acetate membranes increases as high as 25%. Thus, the use of Na-CMC for scaling control can give rise to additional positive effects in desalination of water by reverse osmosis.